(color online) (a) SEM images of Au nanodisks with a diameter from 80 nm to 200 nm. (b) Size-dependent PL from Au nanodisks under 532 nm excitation. In PL measurements, the polarization of excitation is along the horizontal direction and the collection is unpolarized. The numerical aperture of the objective lens is 0.95.^[48] (c) Calculated absorption spectra of Au nanodisks under out-of-plan and symmetric in-plan illumination conditions. (d) Calculated absorption spectra of those relatively large Au nanodisks under right-side in-plan illumination. The inset shows the charge distributions of the 200 nm nanodisk for the fundamental (h^˝) and high-order (h^ˊ) LSPR modes.